1. Field of the Present Invention
The present invention is an improved method for making fluid filled microcapsules.
2. Description of the Prior Art
In the microencapsulation field, it is known to prepare fluid filled microcapsules by use of a submerged extrusion nozzle configuration in which a concentric extrusion nozzle is mounted in a duct through which an inert, immiscible carrier fluid flows. Filler and shell material are extruded from the nozzle into the carrier fluid to form the desired microcapsules. Descriptions of this general type of technique are contained in Microencapsulation: Processes and Applications, edited by Jan E. Vandegaer, Plenum Press, New York, 1973, page 161, and in U.S. Pat. No. 3,389,194 to G. R. Somerville, the latter being incorporated herein by reference. It has been found that under certain process conditions, the integrity of the shell of the microcapsule formed by this technique is compromised so that leakage of fluid filler material occurs.
U.S. Pat. No. 3,423,489 to R. P. Arens et al. relates to a microencapsulation technique in which a carrier fluid is not utilized. This patent indicates that the shell thickness increases as the interfacial tension between the fill and shell is decreased. It teaches that the interfacial tension can often be reduced by the addition of a surfactant to the fill liquid.